TUBE-DRAWING. There are certain peculiarities in the fabrica tion of metal tubes which place them in a separate rank from other manufactures in metal Some varieties of lead-pipe are produced by casting a thick cylinder, of which the internal bore corresponds with the intended bore of the pipe, and then reducing the external diameter by drawing through a series of dies, smaller and smaller as the process proceeds, as described in LEAD MANUFACTURE. Mr. Hick has devised a mode of making tapering tubes ; that is, tubes which taper or diminish in diameter from one end to the other. They are first made parallel or cylindrical and are tapered afterwards; the machine employed effects this by rotating grooved rollers ; and a greater or less degree of taper is ob tained by varying the proportion between the rate at which the tube is drawn through the machine and that at which the rollers revolve. The tubes for many locomotives are made in this way, taper within and cylindrical on the outside ; the metal is cast hollow, and is drawn on a taper mandril through a plate; when used, the thick end is placed nearest to the fire-box. One of the early ways of making wrought iron tubes was to provide a strip of sheet iron, and beat it up by baud Lammers and °wages nearly to a cylindrical form ; this was then laid in a semi-cylindrical cavity, with a mandril running through it ; and then many blows were given by a heavy tilt-hammer, the lower face of which had a hemispherical or rather semi-cylindrical form. An improvement upon this was to draw the tube through grooved rollers after having been thus far fashioned. Another mode afterwards adopted was that of raising a strip of iron to a welding heat ; beating up one end of it nearly to a cylindrical form; drawing the whole piece through a kind of tongs having bell-shaped jaws; and welding without the aid of any mandril. This method has been found available for tubes up to six inches diameter. Common brass tubes are often made by beating a strip of brass round into a cylindrical form, soldering the edges, and drawing it through holes to makethe exterior true; • without paying much regard to the interior. Telescope tubes, &e. are drawn inside and out, and are hardened at the same time ; the soldered tube, being placed upon a steel mandril, is drawn through a draw-plate, by which the tube is lengthened, pressed everywhere close to the mandril, and rendered smooth and dense. Fluted tubes for pencil-cases are drawn through a fluted hole, upon a mandril usually cylindrical Very small tubes, used by silversmiths, are drawn upon steel wire as a mandril. Many
kinds of brass tubes are made exactly in the same way as the lead pipes described in LEAD MANUFACTURE; that is, by casting a thick cylinder, and then drawing it by machinery through a series of holes, smaller and smaller in regular order, so as to elongate the thick cylinder into a thin tube. Mr. Mintz patented a few years ago a process for making tubes of the Hunts metal introduced by him, which metal consists of about 2 parts of zinc to 3 of copper. A short lick tube is cast, and is then rolled out to a great, length and reduced thickness ; but having no mandril within it, it is squeezed flat ; the proper shape is afterwards given to it by drawing through a circular hole. There is something in the quality of the metal which enables it to be elongated in this way, inapplicable to most other kinds. Mr. Webster, of Birmingham, has a curious method of making elastic metal tubes, suitable for forming the junctions of pipes exposed to variable temperature ; or of pipes which are otherwise strained or required to bend, such as the tube couplings connecting locomotives with their tenders, hose with fire-engines, or the like. The tubes are made with traneverso corruga tions, so as to yield to slight bendings, &e. Each corrugation is very narrow and deep. A plain tube is first, and is then corrugated by degrees; this is effected by rolling, the rollers successively used being gradually deeper and deeper in their grooves, until the exterior of the tube is well puckered. Such a tube may be stretched, contracted, or bent within certain limits, without injury to its strength or soundness ; they imitate iu a humble way the snake-like structure. Triangular and rectangular tubes are much used in France for sliding scales and measures; these are made nearly in the same way as ordinary cylindrical tubes, the sectional form being dependent on the draw-hole and the mandril. The small collapsible colour-tubes, Bo much used by artists, were 'at first made like common brass and lead pipes, by successively drawing a thick tube till it becomes very long and very thin; but they are now made more quickly by a peculiar kind of stamping, only possible with such a soft metal as tin. Mr. Ritchie has devised a mode of making tubee thicker at the middle than the ends, by giving them a reciprocating motion between rollers, half way through and back again. - .
Plans have been devised for making copper tubes by electro-deposit. The method will be understood from the principles explained under ELECTRO-METALLITROY.